Rubiaceae and some of its’ species on the uMngeni Estuary
Rubiaceae
and some of its’ species on the uMngeni Estuary
There are
two species along the River and they also grow along the KZN Coastal belt.
These are Psychotria capensis Black
Bird-berry and Pavetta lanceolata
(Weeping Bride’s bush) They belong to this huge family Rubiaceae that goes back
to the Eocene, which was 34 to 56 million years ago. The dinosaurs had just
become extinct. During the Eocene, greenhouse gases (carbon dioxide and
methane) played an important role in controlling surface temperatures. The
diversity for this family is greater in the humid tropics. Coffea
(coffee) belongs to this family as does Chinchona
(quinine).
Pavetta lanceolata is a shrubby plant that grows from about 2-4m.
It grows in full sun. It has beautiful masses of scented white flowers, hence
it’s common name, like confetti. These occur in mid-summer.
Pavetta might come from the word
pauvatta, a Sinhalese (Sri Lanka) vernacular word for this genus. There is also
another interesting possible meaning. Pavimentum is Latin for pavement/bricks/stones.
Therefore a mosaic. This could refer to the scattered bacterial nodules that
are visible on the leaves.
Psychotria capensis grows in half-sun. It gets to about 2-3m
high. Looks better growing in a clump with a tree, or other bushes. The flowers
are little yellow ones that come from August to January and the berries (from
yellow to black to red) from January to July. The black-eyed bulbuls (topies)
adore them. This word comes from the
Greek and it means vivifying, to give or endow life. In the Amazon, there are
many species that are used by the shamans for a variety of purposes.
Along the
river, the bacterial nodules are more visible on Pavetta lanceolata. Other Psychotria
species have more scattered nodules. Bacterial nodules are small swellings
which houses symbiotic bacteria, which fix atmospheric nitrogen, into a form
that the plants can use. There are about 500 flowering species in the Rubiaceae
worldwide, that have these endosymbionts. These symbionts are known to play a
role in assisting in survival of the host. The loss of this bacterial partner/endophyte
affects growth and development of the host plant, suggesting an altered phytohormonal
balance.
The
ancestors of this leaf -nodulated bacteria-plant association originated probably
about 13 Million years ago, during the Miocene (5-23 Million years). 15 Million
years ago, the land mass, which is known today, as Antarctica, split from
Gondwana. It went to the South Pole. In doing so, it left behind the warm
currents of the tropics and the climatic conditions changed so much, that massive
ice-sheets began to be formed. This also happened in the Arctic. Aridification
started in Africa and Asia. The sea-levels and temperatures, around the world
started to drop. As a result of a drier
climate, many plants died out, or had to adapt. It is possible to assume that
climatic change was a possible trigger to promote the bacteria-plant
associations, among leaf-nodulated species, in Africa and Asia. The nodules
might have become a safe haven for soil bacteria that were confronted with drier
habitats. The plant, in turn, had enhanced growth, while it was under
drought-stress. As Antarctica started to melt, around 5 million years ago, so
the sea-levels rose.
References:
Boon, R.
2010. Pooley’s Trees of Eastern South Africa. A Complete Guide. Flora
&Fauna Publications Trust, Durban
Glen, H.
2004. Sappi What’s in a Name? Jacana, Johannesburg
Nichols, G. 2002.
Down to Earth: Gardening with Indigenous Shrubs. Struik
Norman, N
& Whitfield, G. 2006. Geological Journeys. Struik. Cape Town
Photograph
Notes:
The Pavetta
and Psychotria flowers from http://
site
The Pavetta
leaves taken by Kerry-lynn Rieckhoff
Glossary:
Endophyte – an organism that lives within another, without causing disease
Phyto – plants
Symbiotic – a close, prolonged association between 2 or more different
organisms of different species that may but does not necessarily benefit each
one
by Rosemary Harrison
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